Method of producing pulps from lignocellulose containing materials



M y 1969 A. J. A. ASPLUND ETAL 3,446,699

METHOD OF PRODUCING PULPS FROM LIGNOCE'LLULOSE CONTAINING -MATERIALS Original Filed March 51, 1964 United States Patent 3,68 Int. Cl. D21c 3/26, 3/12 US. Cl. 162-19 2 Claims ABSTRACT OF THE DISCLOSURE This invention provides a method of producing mechanical and chemo-mechanical or semichemical pulp from lignocellulose containing material. The continuous method of this invention includes the digesting of the material in the presence of sodium sulfite at a temperature of between 140-240" C. at a superatmospheric pressure. The digested material is defibrated in an atmosphere of steam under substantially the same superatmospheric pressure and temperature prevailing in the digester. At least two successive refining zones are provided after the defibrating step. Progressively decreasing superatmospheric pressures are established and maintained in respective successive refining zones after the said defibrating zone. This causes the defibrated pulp to move from the defibrating zone to and through the successive refining zones. A diluting liquid is introduced into the system before each successive zone. This diluting liquid has a temperature below that prevailing in each preceding stage of the operation to gradually reduce the temperature and consistency of the pulp previous to every new refining zone.

The application is a continuation of applicants copending Ser. No. 356,124, filed Mar. 31, 1964, and now abandoned.

Background of the invention During recent years much work has been devoted to the production with high yield of cellulose pulps by either purely mechanical defibration and/or refining or a combination of chemical treatment and/or partial decomposition and subsequent mechanical defibration of finely divided, lignocellulose containing material, such as wood chips, for example.

Summary of the invention Thepresent invention is primarily based on the defibrating method invented by Arne Johan Arthur Asplund and disclosed in his US. Patents Nos. 2,008,892 and 2,145,851. According to said disclosures the starting material, such as the wood chips, can be defibrated with low consumption of power, when the difibration is conducted at high temperature and under high pressure such as a temperature between 140 and 240 C. and a corresponding steam pressure. After the defibration .the material is subjected to a further treatment generally defined as the refining process.

The defibration may be conducted in the presence of, or without, chemicals or the chips may be decomposed partially by acid or alkaline cooks. The chips may be pretreated by a heating or partial decomposition either in a liquid phase or a vapor phase. In the former case free liquid is removed from chips prior to the defibration; in the latter case no free liquid is present. The defibration is effected immediately after the pre-treatment of the chips and usually at the temperature and under the pressure prevailing in the pre-treatment although it is, of

course, possible to conduct the difibration at both lower and higher temperatures than those prevailing during the pre-treatment.

Since very small quantities of liquid only are present in the difibration procedure and this liquid is taken up by the chips, the defibration is carried out at a high concentration amounting to between 25 and 40 percent, which together with the prevailing high temperature rendering the lignine plastic is the main explanation for the low demand on power for effecting the defibration.

Many plants for production of chemo-mechanical or semichemical pulp have been built according to said principle. Under the conditions prevailing in the defibration process with its high concentration and high temperature, the defibration cannot, however, be advanced to any higher degree of refining without deterioration of the fibers, and hitherto this refining procedure has been conducted in a conventional manner by diluting the pulp to a concentration of 3 to 10 percent and refining it at temperatures below C.

Tests have, however, shown that the refining process may with advantage be conducted in direct sequence to the defibration in such a manner that the defibrated pulp is directly blown into the refining system without collection and dilution in intermediate bins, 'whereby the time interval between the defibration and the refining procedures is reduced to a minimum. The refining process is conducted or at least commenced before the lignine has lost its plastic properties, which results in improved fiber qualities and improved disintegration of the fibers themselves. The refining operation is effected under pressure, but it is obvious that it must be done under less severe conditions than the defibration proper, which means at a lower temperature and with a lower concentration.

The best results are obtained when the refining process is conducted in two or more steps or stations each consisting of a refiner or raffinator, the concentration of the pulp and the temperature being reduced gradually in response to the increase of the grade of grinding in the various steps. By sluices or throttles between the various steps the pressure fall is adjusted so as to be at least so great as to allow the pulp to be passed over from one step to the following Without the use of pumps or similar means. If, however, a minor complete refining of the defibrated pulp is satisfying the refining procedure may be conducted in one single step.

Purpose of the invention It is thus one main object of the invention to provide a method of producing pulp from lignocellulose containing material which in comparison to the methods hitherto used renders improved quality of the fibers and improved disintegration of the individual fiber.

A further object of the invention is to provide a method of producing pulp from lignocellulose containing material which offers possibility of conducting the refining process without additional pumping work.

A still further objection of the invention is to provide a method of producing mechanical or semichemical pulp with reduced consumption of power for attaining a predetermined grade of grinding of the defibrated and refined material.

Brief description of drawing Further objects and advantages of the invention will become apparent from the following description considered in connection with the accompanying drawing showing as example a diagrammatic lateral projection of an apparatus suitable for carrying out the method is shown.

Description of specific embodiment Referring to the drawing the material to be treated is continuously fed through a hopper and a sluice member, for example a so-called cell-feeder 12, to a cooker 14. The material may be constituted by chips of fur wood, for example, which chips have been moistoned with steam and impregnated with an aqueous solution of sodium sulfite having a pH of 6.5 corresponding to kilograms of Na O per ton of chips, calculated as absolutely dry. Fed into the cooker 14 is also steam entering through a pipe 16 so as to create a pressure of 8 superatmospheric atmospheres and a temperature of about 175 C., to exist in the cooker. The chips are treated under a short time, such as five minutes whereupon they are fed at the prevailing temperature and pressure continuously into a defibrator 18, which preferably is of a disc type and driven by an electric motor 20. The defibrator may be of the kind disclosed in the U.S. Patent No. 2,964,250. In the defibrator the chips are decomposed into minor fiber bundles and furthermore individual fibers are set free to some ex- 9 tent.

The pulp suspension has a consistency of about per cent when leaving the defibrator 18 and is blown through a throttle or reducing valve 22 and a conduit 24 under utilization of the high pressure prevailing in the defibrator, into a refiner 26 driven by an electric motor 28 and having a lower pressure prevailing therein such as a pressure of 3 superatmospheric atmospheres. Through a conduit 29 water having a temperature of about 100 C. is supplied immediately before the refiner 26, so as to cause the concentration of the pulp in the suspension to be reduced to 20 percent, for example. Further the temperature of the pulp is lowered to about l-l40 C. After a grinding operation in the refiner 26 the pulp is blown under utilization of the superatmospheric pressure through a throttle or a reducing valve 30 through a conduit 32 into a second refiner driven by an electric motor 42. The pressure in the refiner 40 may be reduced to 2 superatmospheric atomspheres. At the same time water is supplied through a pipe 44, said water having a temperature lower than 100 C., such as C. The pipe 44 debouches ahead of the refiner 40 so as to give to the pulp suspension a consistency of a still lower concentration, which may be about 8 percent, for example, at a temperature of about C. The finally treated pulp escapes through a sluice 46 into an escape opening 48 and is collected in a pulp bin 50. From there the pulp is conveyed through a conduit 52 and a pump 54 to a following station of treatment.

In the refiners or rafiinators 26 and 40 a further separation of the individual fibers of the pulp from one another is elfected together with the disintegration of the individual fibers. These refiners or raffinators may be of principally the same kind as the defibrator 18 and differ therefrom mainly by the grinding members thereof, such as grinding discs, being adapted to accomplish an increased decomposition of the fiber bundles and the fibers into their constituents.

In same cases bleaching chemicals and/or hydrating agents may be added in one or several of the refining steps and they are then suitably added immediately ahead of the grinding discs. The kind of these chemicals depends on the treatment of the chips or the type of the pulp to be produced. If, for example, the pre-treatment consists in a partial decomposition by means of a solution of sulfite, there may be used sulfite, S0 and hydrosulfite. If, on the contrary, the defibration is conducted in the presence of alkaline solutions hydrogen peroxide or sodium peroxide maybe used. Due to the fact that the bleaching is effected under pressure at high temperature and/or concentration, an effect bleaching may be conducted directly in the refining system.

If the chips are decomposed with larger quantities of cooking chemicals, which for some reason or another must be recovered or made non-dangerous, the dilution of the pulp during the refining operation may be to advantage be effected by means of recovered waste liquid.

While one more or less specific embodiment of the invention has been shown and described, it is to be understood that this is for purpose of illustration only and that the invention is not to be limited thereby.

We claim:

1. A method of continuously producing chemo-mechanical and semichemical pulp from lignocellulosic material which comprises, in combination:

(a) digesting the material with sodium sulfite at a temperature of between -240 C. and a corresponding superatmospheric pressure,

(b) defibrating the digested material in a defibrating zone having an atmosphere of steam under substantially the same superatmospheric pressure prevailing in the digester to form a coarse pulp of from about 25 to 40% consistency,

(c) providing at least two successive refining zones after said defibrating zone,

(d) blowing the pulp through a pressure sealed conduit to the successive zones by the pressure prevailing in the defibrating zone, said successive refining zones having respectively decreasing superatmos pheric pressures to cause the defibrated pulp to move from the defibrating zone to and through the successive refining zones,

'(e) introducing a diluting liquid before each successive zone,

(f) said diluting liquid having a temperature below that prevailing in each preceding stage of the op eration to gradually reduce the temperature and consistency of the pulp before each new refining zone.

2. The method according to claim 1, in which a chemical composition consisting of a bleaching and hydrating agent is introduced in at least one of said refining zones.

. References Cited UNITED STATES PATENTS 2,641,164 6/1953 Hill 162-4 

